Plasma reactors are used in processing a workpiece such as a semiconductor wafer in various plasma processes such as plasma etch processes, plasma deposition processes and plasma immersion ion implantation, for example. Reduction in semiconductor device feature size has required improvement of plasma reactors and processes to reduce non-uniformities in plasma processing results. For example, in plasma etch processes, radial distribution of etch rate across the wafer has been successfully reduced below about 5%. As device feature size continues to shrink to 45 nm and then to 32 nm, further improvement in plasma uniformity is needed.